JEE Questions for Physics Electromagnetic Induction Quiz 7 - MCQExams.com

A coil of inductance 40 henry is connected in series with a resistance of 8 ohm and the combination is joined to the terminals of a 2 volt battery. The time constant of the circuit is
  • 40 sec
  • 20 sec
  • 8 sec
  • 5 sec
A capacitor is fully charged with a battery. Then the battery is removed and a coil is connected with the capacitor in parallel, current varies as
  • Increases monotonically
  • Decreases monotonically
  • Zero
  • Oscillates indefinitely
In the figure magnetic energy stored in the coil is
Physics-Electromagnetic Induction-68968.png
  • Zero
  • Infinite
  • 25 joules
  • None of these
In an LR-circuit, time constant is that time in which current grows from zero to the value (where I0 is the steady state current)
  • 0.63 I0
  • 0.50 I0
  • 0.37 I0
  • I0
The coefficient of mutual inductance of two coils is 6 mH. If the current flowing in one is 2 ampere, then the induced e.m.f. in the second coil will be
  • 3 mV
  • 2 mV
  • 3 V
  • Zero
A L – R circuit has a cell of e.m.f. E, which is switched on at time t = 0. The current in the circuit after a long time will be
  • Zero
  • 2)
    Physics-Electromagnetic Induction-68971.png

  • Physics-Electromagnetic Induction-68972.png

  • Physics-Electromagnetic Induction-68973.png
Two coils are placed close to each other. The mutual inductance of the pair of coils depends upon
  • The currents in the two coils
  • The rates at which currents are changing in the two coils
  • Relative position and orientation of the two coils
  • The materials of the wires of the coils
When the current changes from +2A to –2A in 0.05 second, an e.m.f. of 8 V is induced in a coil. The coefficient of self-induction of the coil is
  • 0.1 H
  • 0.2 H
  • 0.4 H
  • 0.8 H
An inductance L and a resistance R are first connected to a battery. After sometime the battery is disconnected but L and R remain connected in a closed circuit. Then the current reduces to 37% of its initial value in
  • RL sec
  • R / L sec
  • L / R sec
  • 1 / LR sec
Why the current does not rise immediately in a circuit containing inductance?
  • Because of induced e.m.f.
  • Because of high voltage drop
  • Because of low power consumption
  • Because of Joule heating
In L – R circuit, for the case of increasing current, the magnitude of current can be calculated by using the formula

  • Physics-Electromagnetic Induction-68976.png
  • 2)
    Physics-Electromagnetic Induction-68977.png

  • Physics-Electromagnetic Induction-68978.png

  • Physics-Electromagnetic Induction-68979.png
The current through choke coil increases from zero to 6 A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is
  • 5 H
  • 2.5 H
  • 1.5 H
  • 2 H
A coil of N = 100 turns carries a current I = 5 A and creates a magnetic flux ɸ =10–5 Tm–2 per turn. The value of its inductance L will be
  • 0.05 mH
  • 0.10 mH
  • 0.15 mH
  • 0.20 mH
Two identical induction coils each of inductance L joined in series are placed very close to each other such that the winding direction of one is exactly opposite to that of the other. What is the net inductance
  • L2
  • 2L
  • L /2
  • Zero
The adjoining figure shows two bulbs B1 and B2, resistor R and an inductor L. When the switch S is turned off
Physics-Electromagnetic Induction-68983.png
  • Both B1 and B2 die out prodietly
  • Both B1 and B2 die out with some delay
  • B1 dies out promptly but B2 with some delay
  • B2 dies out promptly but B1 with some delay
If a current of 5 A in a coil of self-inductance 2 mH is cut off in time 0.1 s, the induced e.m.f. in the coil is
  • 0.1 V
  • 0.01 V
  • 0.2 V
  • 0.02 V
Which types of losses do not occur in the transformer?
  • Iron losses
  • Copper losses
  • Mechanical losses
  • Flux leakage
An AC generator of 220 V having internal resistance r = 10 Ω and external resistance R= 100 Ω. What is the power developed in the external circuit
  • 484 W
  • 400 W
  • 441 W
  • 369 W
In step-up transformer, relation between number of turns in primary (Np) and number of turns in secondary (Ns) coils is
  • Ns is greater than Np
  • Np is greater than Ns
  • Ns is equal to Np
  • Np = 2Ns
The pointer of a dead-beat galvanometer gives a steady deflection becauses
  • Eddy currents are produced in the conducting frame over which the coil is wound
  • Its magnet is very strong
  • Its pointer is very light
  • Its frame is made of abonite
The device that does not work on the principle of mutual induction is
  • Induction coil
  • Motor
  • Tesla coil
  • Transformer
A transformer rated at 10 kW is used to connect a 5 kV transmission line to a 240 V circuit. The ratio of turns in the windings of a transformer
  • 5
  • 20.8
  • 104
  • 40
A current of 5 A is flowing at 220 V in the primary coil of a transformer. If the voltage produced in the secondary coil is 2200 V and 50% of power is lost, then the current in the secondary will be
  • 0.25 A
  • 0.5 A
  • 2.5 A
  • 5 A
Choke coil works on the principle of
  • Transient current
  • Self-induction
  • Mutual induction
  • Wattless current
A transformer of efficiency 90% draws an input power of 4 kW. An electrical appliance connected across the secondary draws a current of 6A. The impedance of the device is
  • 60 Ω
  • 50 Ω
  • 80 Ω
  • 100 Ω
  • 120 Ω
The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following conditions is correct
  • Lines of force minimum but induced e.m.f. is zero
  • Lines of force maximum but induced e.m.f. is zero
  • Lines of force maximum but induced e.m.f. in not zero
  • Lines of force maximum but induced e.m.f. is also maximum
The turn ratio of a transformers is given as 2 : 3. If the current through the primary coil is 3 A, thus calculate the current through load resistance
  • 1 A
  • 4.5 A
  • 2 A
  • 1.5 A
Armature current in dc motor will be maximum when
  • Motor has acquired maximum speed
  • Motor has acquired intermediate speed
  • Motor has just started moving
  • Motor is switched off
The armature of dc motor has 20 Ω resistance. It draws current of 1.5 ampere when run by 220 volts dc supply. The value of back e.m.f. induced in it will be
  • 150 V
  • 170 V
  • 180 V
  • 190 V
In an induction coil, the secondary e.m.f. is
  • Zero during break of the circuit
  • Very high during makes of the circuit
  • Zero during make of the circuit
  • Very high during break of the circuit
The number of turns in the coil of an ac generator is 5000 and the area of the coil is 0.25 m2. The coil is rotated at the rate of 100 cycles/sec in a magnetic field of 0.2 W/m2. The peak value of the e.m.f. generated is nearly
  • 786 kV
  • 440 kV
  • 220 kV
  • 157.1 kV
In a dc motor, induced e.m.f. will be maximum
  • When motor takes maximum speed
  • When motor starts rotating
  • When speed of motor increases
  • When motor is switched off
Work of electric motor is
  • To convert ac into dc
  • To convert dc into ac
  • Both (a) and (b)
  • To convert ac into mechanical work
In an induction coil with resistance, the induced e.m.f. will be maximum when
  • The switch is put on due to high resistance
  • The switch is put off due to high resistance
  • The switch is put on due to low resistance
  • The switch is put off due to low resistance
The induction coil works on the principle of
  • Self-induction
  • Mutual induction
  • Ampere's rule
  • Fleming's right hand rule
An electric motor operates on a 50 volt supply and a current of 12A. If the efficiency of the motor is 30%, what is the resistance of the winding of the motor
  • 6 Ω
  • 4 Ω
  • 2.9 Ω
  • 3.1 Ω
A motor having an armature of resistance 2 Ω is designed to operate at 220 V mains. At full speed, it develops a back e.m.f. of 210 V. When the motor is running at full speed, the current in the armature is
  • 5 A
  • 105 A
  • 110 A
  • 215 A
A transformer is employed to
  • Obtain a suitable dc voltage
  • Convert dc into ac
  • Obtain a suitable ac voltage
  • Convert ac into dc
What is increased in step-down transformer?
  • Voltage
  • Current
  • Power
  • Current density
In a transformer 220 ac voltage is increased to 2200 volts. If the number of turns in the secondary are 2000, then the number of turns in the primary will be
  • 200
  • 100
  • 50
  • 20
The ratio of secondary to the primary turns in a transformer is 3 : 2. If the power output be P, then the input power neglecting all losses must be equal to
  • 5 P
  • 1.5 P
  • P
  • 2/5 P
A step-down transformer is connected to 2400 volts line and 80 amperes of current is found to flow in output load. The ratio of the turns in primary and secondary coil is 20 : 1. If transformer efficiency is 100%, then the current flowing in primary coil will be
  • 1600 A
  • 20 A
  • 4 A
  • 15 A
A loss free transformer has 500 turns on its primary winding and 2500 in secondary. The meters of the secondary indicate 200 volts at 8 amperes under these conditions. The voltage and current in the primary is
  • 100 V, 16 A
  • 40 V, 40 A
  • 160 V, 10 A
  • 80 V, 20 A
An ideal transformer has 100 turns in the primary and 250 turns in the secondary. The peak value of the ac is 28 V. The r.m.s. secondary voltage is nearest to
  • 50 V
  • 70 V
  • 100 V
  • 40 V
The alternating voltage induced in the secondary coil of a transformer is mainly due to
  • A varying electric field
  • A varying magnetic field
  • The vibrations of the primary coil
  • The iron core of the transformer
A 100% efficient transformer has 100 turns in the primary and 25 turns in its secondary coil. If the current in the secondary coil is 4 A, then the current in the primary coil is
  • 1 A
  • 4 A
  • 8 A
  • 16 A
The efficiency of transformer is very high because
  • There is no moving part in a transformer
  • It produces very high voltage
  • It produces very low voltage
  • None of the above
A stepdown transformer reduces the voltage of a transmission line from 2200 V to 220 V. The power delivered by it is 880 W and its efficiency is 88%. The input current is
  • 4.65 mA
  • 0.465 A
  • 0.4545 A
  • 4.65 A
The coils of a step down transformer have 500 and 5000 turns. In the primary coil an ac of 4 ampere at 2200 volts is sent. The value of the current and potential difference in the secondary coil will be
  • 20 A, 220 V
  • 0.4 A 22000 V
  • 40 A, 220 V
  • 40 A, 22000 V
A power transformer is used to step up an alternating e.m.f. of 220 V to 11 kV to tansmit 4.4 kW of power. If the primary coil has 1000 turns, what is the current rating of the secondary? Assume 100% efficiency for the transformer
  • 4 A
  • 0.4 A
  • 0.04 A
  • 0.2 A
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